Method for forming a superhard carbonaceous protective film on articles

Abstract

Proposed is an improvement in the process for forming a superhard carbonaceous coating film on various articles by the plasma-induced CVD method using an apparatus in which microwaves generated in an oscillator are introduced into the CVD chamber through a waveguide duct partitioned from the CVD chamber by a gas shield. In the apparatus used according to the invention, a microwave-barrier diaphragm having an orifice of a limited open area is provided between the gas shield in the waveguide duct and the CVD chamber to form a plasma-generating zone between the gas shield and the microwave-barrier diaphragm so that the intensity of the microwaves directly entering the CVD chamber is so limited that the carbonaceous coating film deposited on the substrate surface can be imparted with greatly increased luster and clarity along with an advantage that the substrate article is subjected to less thermal damage by virtue of the decreased temperature elevation by virtue of the limited intensity of the microwaves reaching the substrate.

What is claimed is: 
     
       1. In a method for forming a superhard carbonaceous coating film on the surface of an article by the plasma-induced chemical vapor-phase deposition (CVD) process in an apparatus comprising a microwave oscillator to generate microwaves, a plasma-induced CVD chamber into which a hydrocarbon compound in a gaseous form is introduced and plasma of the gas is generated to effect deposition of a carbonaceous film on the surface of an article, and a waveguide duct partitioned from the CVD chamber by a gas-shield, through which the microwaves generated in the microwave oscillator are introduced into the CVD chamber, the improvement which comprises providing a microwave-barrier diaphragm having an orifice between the gas shield in the waveguide duct and the CVD chamber to form a plasma-generating zone therebetween so as to limit the microwaves directly entering the CVD chamber. 
     
     
       2. The improvement as claimed in claim 1 in which the microwave-barrier diaphragm is made from stainless steel. 
     
     
       3. The improvement as claimed in claim 1 in which the microwave-barrier diaphragm has a thickness in the range from 1 mm to 5 mm. 
     
     
       4. The improvement as claimed in claim 1 in which the orifice in the microwave-barrier diaphragm has an area which is in the range from 0.1% to 1.2% of the cross sectional area of the waveguide duct. 
     
     
       5. The improvement as claimed in claim 1 in which the orifice in the microwave-barrier diaphragm has a circular form or an elliptic form with the longer axis in the horizontal direction and the shorter axis in the vertical direction, of which the ratio of the longer axis to the shorter axis does not exceed 8:4. 
     
     
       6. The improvement as claimed in claim 1 in which the distance between the gas shield in the waveguide duct and the microwave-barrier diaphragm is in the range from 90 mm to 120 mm along the waveguide duct.